Trenchless technology is the generic name given to all such construction techniques that are used to develop, and maintain subsurface utility networks. The common feature in all these techniques is their requirement of minimum ground surface excavation or destruction. They have been developed over a period of time with the improvisation or combinations of conventional construction techniques. For an example by improvisation of precast piling process, moling or pipe ramming can be derived. The change is that in case of later the driving force is applied horizontally whereas in piling the same is vertical. Similarly cast in-situ piling and auger boring or microtunneling fall in the same envelope on similar lines. The resulting structures again will be similar to a limited extent. Say if one has to just create a hole in the ground to pass a cable, any of the these method can be utilized but if that hole is to pass a gravity flow sewer line the true grade and alignment becomes imperative and one may have to select a technique capable to deliver the desired result from amongst the set of several techniques with similar results.

Technology stream being relatively new, there is a lack of sensitization in the stakeholders about finer nuances of trenchless techniques. This lack of sensitization in turn may lead to an inappropriate technology selection and to avoid such mistakes the engineers must have the understanding of the basics of Trenchless Techniques so that they are able to take appropriate decision while selecting the construction technology.

In addition to the basic understanding of the technique the engineer selecting technology must have the understanding of the duty conditions, site constraints, equipment requirements and the technocommercial matters that have major impact over technology selection process. Selecting any trenchless technique without appropriate understanding of background runs the risk of partial or complete failure. To avoid such failures the need would be the user sensitization about the above issues and Trenchless Technology Selection Guidelines is one of the outcomes of the defending Trenchless Initiative undertaken by IndSTT. The guidelines presented in this compilation attempts to provide directions to such engineers for selecting trenchless techniques for a specific set of duty conditions.

These have been developed on the basis of published data in public domain, reference manuals, and inputs provided by the Guideline Formation Committee and Standards Working Group. They provide the information about different constraints and aim to develop a structured approach in the technology selection process. They are meant to be a comprehensive help in project planning and execution, intended for engineers engaged in such activities and having the basic understanding of the utility or subsurface construction and management processes. It is also aimed at providing guidance to project planners for evaluating the selection process so that any unexpected action at a later date, may be during the construction or during operations can be avoided.

The guidelines presented in this document are based on the existing trenchless methods for creating and renewing subsurface utility installations. This document has been developed using information available from field and other sources and is expected to be suitable for most situations encountered in general subsurface construction works. The document, by no means, endorses or recommends any specific technique. It merely informs the reader about the suitability of a specific technique for a given site conditions and is based on the sound engineering practices and past experiences and reports. The reader must understand that particular conditions, projects or localities may require special or different practices that might not have been covered in these guidelines. Moreover underground construction projects present many risks and there is no guarantee that the techniques selected on the basis of these guidelines will be successful all the times at all the project and site conditions. Reader should consider risks involved and assume appropriate contingencies in the projects. Design engineers must be involved in the project design and documentation activities.

Importance of trained and certified equipment operators also can never be underestimated as their skills are the most vital inputs of any successful trenchless project. We must remember that in spite of taking all the correct decisions, machine operatorís inability in delivering the project will lead to a failed project. The guidelines, therefore also include the minimum Vocational Qualifying Criterion (VQC) for two most common trenchless techniques being used currently. In addition to providing a yardstick for the operatorís qualifications these also inform the user about the inputs of the technique and enables him to understand the technique requirements in a better way. IndSTT in due course shall be developing VQCs for other techniques and the same will be included in the subsequent editions of this guidelines.

IndSTT wishes to convey its thanks to the Defending Trenchless and Guideline formation Committee members for the support extended and providing the much required inputs for these guidelines. It also invites the reader to provide his inputs for inclusion in the next edition of these guidelines. It is hoped that these guidelines would be immensely useful for the Trenchless Industry and able to reduce the element of project risk.

Dr. Niranjan Swarup
Director General
Indian Society for Trenchless Technology